1. Field of the Invention
The present invention relates to unnatural ceramide related compounds and more particularly to unnatural ceramide related compounds useful as intermediates for the preparation of sphingoglycolipids. The present invention also relates to a method for preparing the ceramide related compounds.
2. Description of the Prior Art
The glycolipid of mammalian cells belongs to the category of so-called sphingoglycolipid and comprises (i) a lipid structure referred to as ceramide composed of a long-chain aminoalcohol called sphingosine to which a fatty acid is amido-bonded and (ii) various combinations of sugars selected from the group consisting of glucose, galactose, N-acetylglucosamine, N-acetylgalactosamine, fucose and sialic acid which are bonded to the structure through glycoside bonds. Among these, the glycolipids carrying sialic acids are called gangliosides.
Most of these compounds are generally located in the outerside layer of the double layer of cell membrane and it has been thought from recent investigations that these compounds play important roles in the functions as a reception, response and receptor of recognition and information, differentiation, proliferation, malignant change, or behavior of cells.
However, it is quite difficult to isolate such sphingoglycolipids from an organism and to purify it. Therefore, the precise synthesis of the aforementioned ceramide related compounds is necessary and indispensable for the elucidation of the relationship between the precise biological information of these sugar chains and the molecular structure thereof.
Under such circumstances, the inventors of this invention have already developed a method for stereospecifically preparing these glycolipids, in particular natural ceramide moieties in a good yield (see Japanese Patent Un-examined Publication, hereunder referred to as "J. P. KOKAI" for simplicity, No. 60-190745).
Moreover, the natural sphingosine is an optically active compound of D-series (2S, 3R) of erythro arrangement and various methods for preparing the same have presently been proposed, in which D-glucose or L-serine is used as a starting material.
Moreover, there has been proposed, by Grob C. A. (Helv. Chim. Acta, 1957, Vol. 40, p. 1145), a method for preparing an unnatural ceramide such as a trans-DL-threo isomer or a cisDL-threo isomer in which an achiral compound is used as a starting material.
However, in the conventional methods, all the processes for obtaining final products, i.e., unnatural and natural ceramides, are carried out using materials in the form of racemate forms, although the optical resolution of the final products is very difficult.